1. Field of the Invention
This invention broadly relates to a method for orienting an orthodontic appliance, such as a bracket or buccal tube, to a tooth. More particularly, the present invention is concerned with a method for selecting the relative orientation of an orthodontic appliance that is adapted to be directly bonded to a tooth by an adhesive.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to orthodontically correct locations. Orthodontic treatment can result in improved occlusion, so that the teeth properly function with other teeth in a satisfactory manner during mastication. Orthodontic treatment can also greatly enhance the aesthetic appearance of the patient's oral cavity.
One common type of orthodontic treatment involves the use of tiny appliances known as brackets that are often fixed to the patient's anterior, cuspid and bicuspid teeth. An archwire is placed in a slot of each bracket. The archwire forms a track to guide movement of the teeth to desired locations.
Ends of orthodontic archwires are often placed in passages of small appliances known as buccal tubes. In turn, the buccal tubes are fixed to the patient's molar teeth. The brackets, buccal tubes and archwires form an orthodontic system that is commonly known collectively as “braces”.
One popular method of orthodontic treatment is known as the “level-arch” technique, and involves placing the brackets on the patient's teeth at certain selected locations so that the “U”-shaped archwire extends in a generally level plane at the conclusion of treatment. When the archwire is initially installed on the brackets, the malpositioned teeth may cause the wire to deviate from its normally planar configuration (in horizontal view) and from its normally smoothly curved configuration (in plan view). However, the inherent resiliency of the archwire tends to urge the brackets and hence the associated teeth toward a level array wherein the archwire re-assumes its normally planar and smoothly curved configuration. The level-arch technique is considered satisfactory by many orthodontists because the need for bends, steps or other adjustments in the archwire is reduced and in many cases eliminated, resulting in a savings of time for both the orthodontist as well as the patient.
As can be appreciated, the degree of success of the level-arch technique is related in part to the position and orientation of the brackets and buccal tubes on the patient's teeth. For example, if one of the brackets is bonded to a patient's tooth at a location that is too close to the patient's gingiva (i.e., the patient's gums) relative to the placement of brackets on adjoining teeth, that tooth will protrude outwardly an excessive distance in an occlusal direction (i.e., in a direction toward the outer tips of the patient's teeth) relative to adjoining teeth at the conclusion of treatment if all of the brackets are aligned in a level array. In such an instance, the orthodontist can correct the orientation of the malpositioned tooth by placing bends or steps in the archwire at locations adjacent each side of its bracket, but such a practice entails additional work for the orthodontist and may also increase the overall length of treatment time.
As a consequence, many suggestions have been made in the past for improving the placement accuracy of orthodontic appliances during the procedure of bonding the appliances to the patient's teeth. For example, height gauges such as the well-known “Boone” gauge provide a means for indicating a desired position of the appliance on a tooth relative to the occlusal edge of the associated tooth. Another device for improving placement accuracy is known as a positioning device or jig, such as the devices described in U.S. Pat. Nos. 4,455,137, 4,850,864 and 5,429,229. These devices support the appliance on a tooth surface at a location that is a pre-determined distance from the occlusal edge of the tooth.
While the bonding techniques described above are considered satisfactory by some practitioners, there are shortcomings that are inherent with such techniques. For example, access to the surfaces of certain malpositioned teeth (such as the bicuspid and molar teeth) may be difficult. In some instances, and particularly in connection with posterior teeth, the practitioner may have difficulty seeing the precise position of the appliance relative to the tooth surface. Another problem with the above described techniques concerns the significant length of time needed to carry out the procedure of positioning and bonding an appliance to each individual tooth, which is a nuisance both to the patient as well as to the orthodontist. The risk of moisture contamination from the patient's saliva also increases as the time increases that the patient is awaiting completion of the bonding procedure. The above factors may also unduly impair the accuracy of placement of the appliances on the teeth and/or increase the chance that the ultimate adhesive bond will not have sufficient strength to retain the appliances on the teeth during the course of orthodontic treatment.
Bonding techniques known as “indirect bonding” avoid many of the problems noted above. In general, indirect bonding techniques involve the use of a transfer tray having a shape that matches the configuration of at least part of one of the patient's dental arches. A set of appliances is releasably connected to the tray at certain, pre-determined locations. Once adhesive is applied to the base of each appliance, the tray is placed over the patient's teeth until such time as the adhesive hardens. Next, the tray is detached from the teeth as well as from the appliances, often with the result that all of the appliances that were previously connected to the tray are now bonded to their respective teeth at certain intended, pre-determined locations. The procedure is often then repeated for the patient's other dental arch.
In more detail, one known method of indirect bonding includes the steps of taking an impression of the patient's dental arch and then making a replica plaster or “stone” model from the impression. A sealing solution (such as Liquid Foil brand sealing solution from 3M) is applied to the stone model and allowed to dry. If desired, the teeth of the model are marked with a pencil to assist in placing the appliances in ideal positions.
Next, the appliances are temporarily bonded to the sealed stone model. Optionally, the bonding adhesive can be a chemical curing adhesive (such as Concise brand from 3M) or a light curable adhesive (such as Transbond XT or Transbond LR adhesive from 3M). Optionally, the appliances may be adhesive pre-coated brackets such as described in U.S. Pat. Nos. 5,015,180, 5,172,809, 5,354,199 or 5,429,229.
A transfer tray is then made by placing matrix material over the model as well as over the appliances on the model. For example, a plastic sheet matrix material may be placed over the model and appliances and then heated in an oven. A vacuum source is used to evacuate air between the matrix material and the model. As the matrix material is heated, the plastic sheet material is drawn down over the model and assumes a configuration that precisely matches the shape of the replica teeth of the stone model and adjacent appliances.
The plastic model is then allowed to cool and harden to form a tray. Next, the tray and the appliances (which are embedded in an interior wall of the tray) are detached from the stone model, and the sides of the tray are trimmed as may be desired. The tray also may be cut into smaller sections for ease of placement during bonding. If the cured adhesive remains on the appliance base after detaching the appliances from the model, the adhesive can serve as a custom-made bonding surface having a contour that matches the contour of the patient's tooth for a snug, mating fit.
Once the patient has returned to the office, a quantity of adhesive is placed on the base of each appliance (or on the cured adhesive, if any), and the tray (or tray section) with the embedded appliances is then placed over ma tching portions of the patient's dental arch. Since the configuration of the interior channel in the tray closely matches the respective portions of the patient's dental arch, each appliance is ultimately positioned on the patient's teeth at precisely the same location that corresponds to the previous location of the same appliance on the stone model.
Both light-curable adhesives and chemical curing adhesives have been used in indirect bonding techniques to secure the appliances to the patient's teeth. If a light-curable adhesive is used, the tray is preferably transparent or translucent. If a two-component chemical curing adhesive is used, the components can be mixed before application to the appliances, or alternatively one component may be placed on each appliance base (or on the cured adhesive, if any) and the other component may be placed on the tooth surface. In either case, placement of the tray with the embedded appliances on corresponding portions of the patient's dental arches enables the appliances to be bonded to the teeth as a group in a relatively short amount of time. With such a technique, individual placement and positioning of each appliance in seriatim fashion on the teeth is avoided.
U.S. Pat. No. 6,123,544, assigned to the assignee of the present invention, describes improved methods and apparatus for precisely positioning and bonding orthodontic appliances to the teeth. In one embodiment described in that patent, orthodontic appliances are releasably connected to arms that, in turn, are slidably received in passageways of a transfer tray. After the transfer tray is received on one of the patient's dental arches, the arms are moved along the passageways until the adhesive on the appliances comes into contact with the tooth surfaces. The arms provide a means for moving the appliances to certain pre-selected positions on the teeth.
In some of the embodiments described in U.S. Pat. No. 6,123,544, the transfer tray is made by placing analogs of the orthodontic appliances on replica teeth such as a stone model. Each analog is connected to a respective fixture arm, and a quantity of matrix material is then applied to both the replica dental arch and the fixture arms. After the matrix material has hardened, the fixture arms with the appliance analogs are replaced by carrier arms that are releasably connected to the selected appliances.
The resulting location of the orthodontic appliances on the patient's teeth according to the methods and apparatus described in U.S. Pat. No. 6,123,544 is determined in substantial part by the selected orientation of the appliance analog on the replica dental arch. One method of selecting this orientation can be carried out manually by, for example, drawing pencil lines along the replica teeth in a mesial-distal direction, optionally using one of the height gauges described above. As another option, an automated device such as a computer controlled robotic arm may be used to place the appliance analogs on the associated replica teeth, using software and digital information of the replica dental arch to select desired locations of the analogs and ultimately of the selected appliances.
There is a continuing need in the art to further increase the accuracy of placement of orthodontic appliances on the patient's teeth, so that the ultimate positions of the teeth at the conclusion of orthodontic treatment is identical to the positions sought by the orthodontist. In addition, it is desirable that any new method for selecting the orientation of an orthodontic appliance on a tooth be carried out by the use of computer software that would be useful in diagnosis and treatment planning as well as in subsequent manufacturing processes, such as in the fabrication of indirect bonding transfer trays as described above.